Fluids and Oils

We all know about the three main fluids that cars run on: fuel, oil, water (except for aircooled cars). But how often do we think about the other fluids used in the car? (Usually not unless something important fails.)

Brake Fluid

The most important is brake fluid. Most European and Japanese cars require DOT4 brake fluid. We have found that many of the common DOT3 fluids are not compatible with the natural rubber seals used in most of these cars.

If your brake fluid turns black or has black specks in it, this indicates that the rubber is being dissolved or damaged. The softer natural rubber seals perform better than the common domestic synthetic seals, but they are more vulnerable to chemical attack.

See Brake Fluid for excerpts from a Castrol technical bulletin (undated, but still good information) on brake fluids, and our recommendations.

Power Steering Fluid

This is not always what it seems. Most American cars use something that is sold as “Power Steering Fluid.” This has rarely been used in imported cars. Most imports have traditionally used Automatic Trans Fluid in their power steering. Many of the newer European cars are now using hydraulic power systems that require HSMO fluids (see HSMO, above).

Mercedes-Benz has their own special power steering fluid, which we carry under a Mercedes part number, and which is different from their hydraulic system fluid and from everything else that we know about.

Some of the Japanese cars use their own fluids, and I recommend biting the bullet and buying it from the dealer if your manual calls for something special. Power steering pumps and racks and boxes are too expensive to try to cut corners on fluid! (Not to mention that having your steering work correctly is really important.)

The Mercedes fluid, part number 000-989-88-03 comes in 0.5L containers (slightly more than a pint) and sells for $7.95. We also have an alternate brand that sells for $10.95 per liter.

Transmission Fluids

Transmission fluids seem fairly simple — manual transmissions ought to take gear lube, and automatics ATF. But neither is as simple as it looks. See Transmission Fluid.